Just having a browse round our tesco extra and noticed that the Castrol GTX for Diesel engines is only £11.98 for 4 litres. This is not a reduction or anything just their normal price. I usually pay between £15 and £17 for this in Wilkinsons and Halfords have the cheek to charge £19.99!! I checked online but it doesn't seem to be available so instore only they may have it in the petrol stations ???. They also had ordinary Castrol GTX for petrol engines at a good price but I dont remember the exact figure.